On Monday, the mother of Prince George, 4, and Princess Charlotte, 2, made a public appearance only hours after giving birth to her third child, a boy, on the steps of St. Mary’s Hospital in London, wearing a red-and-white custom Jenny Packham dress. That same day, Biel, speaking to Yahoo Lifestyle at her West Hollywood kid-friendly restaurant Au Fudge, says, “I can’t imagine,” about the royal mom. “I also can’t imagine the nylon situation — don’t [royals] have to wear them? Nylons right after the hospital? Forget it! [Middleton] is Superwoman to do that.”

Alba agrees, adding, “After birth, you’re wearing a diaper. And if you had a C-section, you’re wearing more!” (To which Biel adds, “You’re wearing a diaper and a girdle.”)

The two stars joined Yahoo Lifestyle for an exclusive interview on childbirth, breastfeeding judgment, and “rookie” parenting mistakes. Biel has a son Silas, 3, with her husband, Justin Timberlake, and Alba has three children (daughter Honor, 9, daughter Haven, 3, and son Hayes, 3 months) with her husband, Cash Warren. They’d come together to celebrate the new book of their beloved “nanny to the stars,” Connie Simpson, a charismatic baby nurse with a gold-plated client list including Emily Blunt and John Krasinski, andMatt Damon and Luciana Barroso.

As a live-in baby nurse, Simpson wears multiple hats — she’s there for midnight feedings, ride-alongs to the pediatrician, and providing postpartum care, but her role is also part life coach, helping parents navigate the unexpected, such as potential judgment over how they feed their babies. “If you teach women how to be confident at home, then it’s easier for them to go out,” Simpson tells Yahoo Lifestyle at the soiree. “And if you have that confidence, you don’t care what people say … you get the job done and you move on.”

That pressure can often derive from mothers themselves, such as with Biel, who is her own “harshest critic,” she says. “Back in the day, women used to help each other feed their babies. I had a very hard time breastfeeding and getting good amounts of quality fatty milk. For whatever reason,it was just harder for me. And if I had women in my community who I trusted and who would have shared with me — this may freak people out — but I would have 100 percent [had them feed my baby]. … At one point, Connie was begging me to find some formula.”

Adds Alba, “We should normalize breastfeeding. I nursed my son anywhere he wanted to — especially as a newborn, you have to feed them when they want to feed. … I produced a lot of breast milk with my first, but my baby didn’t want to feed on me. My second child was into it, but my milk supply was not as much. And with my third, my supply was not enough for him, so after three weeks I did a combination feed. … It’s OK to feed your child however you need.”

Jessica Alba and Jessica Biel are celebrating a new book written by baby nurse “to the stars” Connie Simpson. (Photo: Rochelle Brodin)

Simpson’s client base is largely but not exclusively celebrities, so she often contends with knee-jerk assumptions about her field of work. “One of the biggest stereotypes about my job is that women don’t need help or that it costs too much,” she says. “It can be expensive, but there’s always somebody in your community who needs extra change — they can come over and give you time to rejuvenate as a parent. Because every parent needs help. You will always run into that wall where you feel like you’re all alone and you need someone.”

However, Biel and Alba initially had different approaches to hiring help. “I was 26 when I got pregnant and 27 when I gave birth,” explains Alba. “I had all these ideas about what having a baby would be like, but the closer I got down to it, I thought, ‘I can’t believe they’re going to let me take this baby home.’ And my [lack of] self-care — I had no idea what having a baby would do to my body. I couldn’t sit down for three weeks. It was awful. I thought I was dying.”

In Biel’s case, the decision to hire Simpson was immediate. “The second I got pregnant, I said, ‘I know I need help,'” she says. “I wasn’t a person who had always dreamed of having a family, and I didn’t have these instincts — I really didn’t know anything. But I knew how important my relationship with my husband is and was, and that [parenthood] would turn our lives upside down, and that I needed to have someone to guide and help me when I needed to go back to work.”

However, Simpson’s job isn’t without its challenges. Moving in with families for a period of up to six months means spending intimate time with people, often strangers, whose viewpoints don’t always align with her goals. “If a parent and I disagree, first I always tell them, ‘Bless your little heart,'” says. “And I’ll say, ‘It’s OK, sweetheart. Let’s do it this way and see if it works.’ It takes years off my life, but I have to be in [the moment] with parents so they can go through it and understand that there is another way.”

Allowing parents to make mistakes and carve their own paths worked for Alba (who says, “I made all the rookie mistakes!”) and Biel, who struggled with finding perspective after the birth of Silas. “Because I had a C-section, I felt so much guilt about the baby not getting the right antibodies,” she says, adding, “It took me forever to figure out this balance of, ‘Well, it’s OK and I’m doing my best.'”